When I answer a reader question over English, I try not to say much. Instead I choose to trust the reader to find out the answers by themselves. This attitude of non-interference, thank you very much, often works.
Here, for example, is a little to-and-fro with Shirlie (who always seems to have another question ready for me the minute I have answered the last one):
Xin: Thanks for writing. Please hit this link (omitted) for reply in detail.
Shirlie: Thank you very much…. But I'm sorry I have to bother you again. This time I'm really confused by some explanation about a 20-minute walk and a 20 minutes' walk. I think they are both right. But some said they are not. Here I copied the original question for you:
3. Every morning Mr. Smith takes a ______ to his office.
A．20 minutes' walk B．20 minute's walk
C．20-minutes walk D．20-minute walk
The answer is A. But others say the answer is D. I think both are right. Some said they chose D because A needn't an article. Is that right? I don't think they are right. What's your opinion?
Xin: Never mind my opinion (it's not a matter of opinion, is it?), the answer is D. Have a good day.
Shirlie: Thanks, but I'm still wondering why A is not right? Even some books say "a 20 minutes' walk" is right.
Xin: May I challenge you to produce the book?
Shirlie: Thank you for your patience. I'm the last one who wants you to be bothered by silly grammatical questions, which drive me crazy sometimes and I'm trying to escape from them. I'm sorry I can not present you the book because the book is not available now, but the website is available. You would say it's stupid to believe in the websites, yap, sometimes it is true. The book won't be available until next week when I go home. So I will make everything clear at that time. The website is here (omitted).
Xin: I'll skip the website in anticipation of the book. Yes, I "would say it's stupid to believe in websites", but I wouldn't say "yap".
These days, one can't even believe in books (which is why I asked you to kindly produce it in the first place), not to mention websites.
Shirlie: I returned home and found out what the book told their readers is: 20 minutes' walk; a 20-minute walk; they are both right. Sorry to have bothered you because of my poor memory.
Xin: Now that you've produced the book, you may look at it this way: If "a 20 minutes' walk" is as good as "a 20-minute walk", "20-minute" as adjective would not have been invented.
To cure from this book, read other books.
Shirlie: Haa, to look at a thing in a different way can be so interesting. Your suggestion is good and I will try it with other problems. Still I have a question: Can "still" modify "others"? Like in this sentence: There are some robots working in factories, others working in the hospitals, ____ (still others/ the others) working in the schools.
Xin: "Still I have a question", as though I didn't know... Now, can "still" modify "others"? Apparently yes. Here, "still" is not a modifier, though. It's an adverb.
An easy example: Some readers ask questions. Others don't. Some ask one question and leave me alone. Some others ask two or more questions but all of them at once. Still others, such as Shirlie, prefer to ask one question after another.
In fact, I'm sure Shirlie has still another one up her sleeve right now, ready to release the moment she reads this.
Got to run...